Underlayer composition and method of imaging underlayer

ABSTRACT

A method of forming a pattern comprises diffusing an acid, generated by irradiating a portion of a photosensitive layer, into an underlayer comprising an acid sensitive copolymer comprising an acid decomposable group and an attachment group, to form an interpolymer crosslink and/or covalently bonded to the surface of the substrate. Diffusing comprises heating the underlayer and photosensitive layer. The acid sensitive group reacts with the diffused acid to form a polar region at the surface, in the shape of the pattern. The photosensitive layer is removed to forming a self-assembling layer comprising a block copolymer having a block with an affinity for the polar region, and a block having less affinity than the first. The first block forms a domain aligned to the polar region, and the second block forms a domain aligned to the first. Removing either the first or second domain exposes a portion of the underlayer.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a nonprovisional of U.S. Provisional Application No.61/389,527, filed on Oct. 4, 2010, the content of which is incorporatedby reference herein in its entirety.

BACKGROUND

Block copolymers may be used in directed self-assembly processes to formpatterns without requiring a photolithographic process. The blockcopolymers can form the patterns by assembling on a neutral or patternedsurface having neutral and polar regions. Such a neutral or patternedsurface can be afforded by use of a polymer brush underlayer.

Polymer brushes are polymeric chains affixed to a surface of a substrateformed of, for example, a semiconductor material. The surface isreactively modified to the desired thickness and surface energy usingpolymer brush precursors with a desired composition. The composition ofa random copolymer underlayer is tuned to afford the desired neutralsurface.

For block copolymers capable of self assembly but for which it isunfeasible to synthesize random copolymers of repeating units of eachblock (such as where different polymerization mechanisms would berequired, or where the composition of the brush copolymer is not),end-group functionalization or incorporation of reactive-groupcontaining monomers in the brush copolymer has been performed. (Seee.g., P. Mansky, Y. Liu, E. Huang, T. P. Russell, C. Hawker,“Controlling polymer surface interaction with random copolymer brushes”,Science, 275, 1458, (1997)). Such compositional modifications to thebrush copolymer are designed to provide functional sites for grafting.However, there is no disclosure in the art of adjusting the brushpolymer composition to change surface polarity lithographically, andhence form a patterned surface on which the self-assembling layer canform.

STATEMENT OF INVENTION

The shortcomings of the prior art are overcome and additional advantagesare provided through the provision of, in an embodiment, a method offorming a pattern comprising irradiating a portion of an underlayercomprising an acid sensitive copolymer comprising an acid decomposablegroup, an attachment group, and a functional group, the attachment groupbeing covalently bonded to a hydrophilic surface of a substrate,crosslinked to form an interpolymer crosslink, or both covalently bondedto the surface of the substrate and crosslinked to form an interpolymercrosslink, and a photoacid generator, wherein the acid decomposablegroup reacts with an acid generated from the photoacid generator in theirradiated portion of the underlayer to form a polar region at a surfaceof the underlayer, the polar region having a shape and dimension of thepattern, forming a self-assembling layer on the surface of theunderlayer, the self-assembling layer comprising a block copolymerhaving a first block with an affinity for the polar region, and a secondblock having less affinity for the polar region than the first block,wherein first block forms a first domain aligned to the polar region,and the second block forms a second domain aligned adjacent to the firstdomain, and removing either the first or second domain to expose anunderlying portion of the underlayer.

In another embodiment, an underlayer comprises an acid sensitivecopolymer comprising an acid decomposable group, an attachment group,and a functional group, and a photoacid generator, wherein theattachment group is covalently bonded to a hydrophilic surface of asubstrate by alkoxide linkages, is crosslinked to form an interpolymercrosslink, or is both covalently bonded to the hydrophilic surface ofthe substrate and crosslinked to form an interpolymer crosslink, andwherein the acid decomposable groups are ester groups, acetal groups,ketal groups, pyrocarbonate groups, or a combination comprising at leastone of the foregoing acid decomposable groups.

In another embodiment, a self-assembled multilayer film, comprises anunderlayer comprising an acid sensitive copolymer comprising an aciddecomposable group, an attachment group, and a functional group, and aphotoacid generator, wherein the underlayer is disposed on andcovalently bonded to a hydrophilic surface of a substrate, crosslinkedto form an interpolymer crosslink, or both covalently bonded to thesurface of the substrate and crosslinked to form an interpolymercrosslink through the attachment group, and portions of a surface of theunderlayer having the acid decomposable groups decomposed to form apatterned surface of the underlayer, and a self-assembling layerdisposed on the patterned surface of the underlayer, the self-assemblinglayer comprising a block copolymer having a first block with an affinityfor the portion of the surface of the underlayer having decomposed aciddecomposable groups, and a second block having less affinity for theportion of the surface of the underlayer having decomposed aciddecomposable groups than the first block, wherein the first block formsa first domain aligned to the portion of the underlayer having thedecomposed acid decomposable groups, and the second block forms a seconddomain on the surface of the underlayer aligned with and adjacent to thefirst domain.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of theinvention are apparent from the following detailed description taken inconjunction with the accompanying drawings in which:

FIGS. 1A-1I show an exemplary method of forming a pattern on aunderlayer in one embodiment in which acid is generated in aphotosensitive underlayer containing a photoacid generator;

FIG. 2 shows atomic force microscopy (AFM) images of an exemplarypatterned self-assembled block copolymer layer on both a brush layerwithout PAG and an imageable mat layer containing a PAG, patterned tohave cylindrical domains.

DETAILED DESCRIPTION

Disclosed herein is a novel brush copolymer underlayer, sometimesreferred to herein simply as an underlayer, for directed self-assemblyof a block copolymer. The underlayer comprises a random copolymercontaining an acid decomposable group, an attachment group, and afunctional group, and a photoacid generator. The proportion of themonomers is adjustable to moderate surface energies to match those of aself-assembling block copolymer which is formed on the surface of theunderlayer. The underlayer copolymer may be bonded to a hydrophilicsurface of a substrate, including a semiconductor substrate such as,e.g., silicon with native oxide or thermally grown oxide, a titaniumdioxide layer, etc., to form the underlayer, may be crosslinked withinterpolymer crosslinks to form a mat layer, or may form both surfacebonds and crosslinks to provide a crosslinked, surface bonded mat layer.

A pattern is formed in the underlayer by including a photoacid generatorin the underlayer and directly irradiating the underlayer to generateacid in the irradiated regions of the underlayer that reacts with theacid sensitive copolymer of the underlayer. The exposure pattern of theunderlayer may be closely (densely or semi-densely) spaced features oflines, dashes or dots, a sparse pattern of widely spaced lines, dashes,or dots, or combinations of irradiated features.

The method further involves overcoating the patterned underlayer with ablock copolymer, annealing the block copolymer so that one block phaseseparates to align over the deprotected portions of the underlayercontaining the acid-decomposed functional groups. A block of the blockcopolymer is then removed using, e.g., a thermal, photochemical, solventor plasma method, to create a pattern.

The underlayer comprises an acid sensitive copolymer. The acid sensitivecopolymer includes as constituent parts an acid decomposable group, anattachment group, and a functional group.

The relative proportions of the constituent groups are selected suchthat a desirable balance of properties of these groups, includingsurface energy and wettability, is obtained for the acid sensitivecopolymer before deprotection, and hence for the underlayer prior to anydeprotection or in regions where the underlayer is not deprotected. Inparticular, where the acid sensitive copolymer has not been deprotected,the underlayer including the acid sensitive copolymer has a neutralsurface energy toward a self-assembling layer based upon a blockcopolymer. As used herein, “neutral” means that the surface energy ofthe underlayer (before deprotection, or in regions where no deprotectionhas occurred) is comparable to that of the block copolymer. Further, theproportions of the constituent groups are selected such that a desirablebalance of properties including layer neutrality of the underlayerbefore deprotection and polarity of the regions of the acid sensitivecopolymer after deprotection, is achieved so that a block copolymerdisposed on the patterned surface will form phase-separated domains byblock, aligned to the surface.

The acid decomposable group is any group that may be chemicallydecomposed by contact with an acid of sufficient activity. In anembodiment, the acid decomposable group is a C₁₋₃₀ acid decomposablegroup comprising an ester group, acetal group, ketal group,pyrocarbonate group, or a combination comprising at least one of theforegoing acid decomposable groups. Alternatively, the acid decomposablegroup may be a crosslinker or crosslinkable group.

In a specific embodiment, the acid decomposable group is a C₄₋₃₀tertiary alkyl ester. Exemplary C₄₋₃₀ tertiary alkyl groups include2-(2-methyl)propyl (“t-butyl”), 2-(2-methyl)butyl, 1-methylcyclopentyl,1-ethylcyclopentyl, 1-methylcyclohexyl, 1-ethylcyclohexyl,2-methyladamantyl, 2-ethyladamantyl, or a combination comprising atleast one of the foregoing. In a specific embodiment, the aciddecomposable group is a t-butyl group or an ethylcyclopentyl group.

The attachment group may be any group containing a reactive functionalgroup capable of forming a bond to a substrate. The bond may be anionic, coordinative (by, e.g., a metal-ligand bond) or covalent bond toa substrate. Preferably, the bond is a covalent bond. The attachmentgroup may be a hydroxy, thiol, or primary or secondary aminesubstituted, straight chain or branched C₁₋₃₀ alkyl, C₃₋₃₀ cycloalkyl,C₆₋₃₀ aryl, C₇₋₃₀ alkaryl, C₇₋₃₀ aralkyl, C₁₋₃₀ heteroalkyl, C₃₋₃₀heterocycloalkyl, C₆₋₃₀ heteroaryl, C₇₋₃₀ heteroalkaryl, C₇₋₃₀heteroaralkyl or a combination comprising at least one of these groups.As used herein, the prefix “hetero” refers to any non-carbon,non-hydrogen atom including, for example, the halogens (fluorine,chlorine, bromine, iodine), boron, oxygen, nitrogen, silicon, orphosphorus, unless otherwise specified. Exemplary attachment groupsinclude 3-aminopropyl, 2-hydroxyethyl, 2-hydroxypropyl, or4-hydroxyphenyl. Alternatively, or in addition to these functionalgroups, other reactive functional groups may be included to facilitatebonding of the acid sensitive copolymer to the surface of a substrate.Exemplary attachment groups include mono-, di- and trialkoxysilanegroups such as 3-propyltrimethoxysilane (obtained by thecopolymerization of other monomers withtrimethoxysilylpropyl(meth)acrylate), glycidyl groups (obtained by thecopolymerization with glycidyl(meth)acrylate), or reactive strainedrings such as benzocyclobutanes (“BCB,” obtained by the copolymerizationwith, for example, vinyl benzocyclobutane) which may ring open to formreactive dienes which can react with olefinic groups on the surface ofthe substrate, or with other ring-opened BCB groups in the polymer toform a dimer. As used herein, “(meth)acrylate” refers to an acrylate,methacrylate, or a combination of these.

The functional group, included to adjust the neutrality of theacid-sensitive copolymer, may be a straight chain or branched C₁₋₃₀alkyl, C₃₋₃₀ cycloalkyl, C₆₋₃₀ aryl, C₇₋₃₀ alkaryl, C₇₋₃₀ aralkyl, C₁₋₃₀heteroalkyl, C₃₋₃₀ heterocycloalkyl, C₆₋₃₀ heteroaryl, C₇₋₃₀heteroalkaryl, C₇₋₃₀ heteroaralkyl or a combination comprising at leastone of these groups. The functional group may be unsubstituted, or maybe substituted with a further functional group including halogen such asfluorine, chlorine, bromine, or iodine; a hydroxy group; an amino grouphaving the structure —N(R′)₂, where each R′ is independently H, cyclicor acyclic C₁₋₃₀ alkyl or C₃₋₃₀ aryl, or fused C₂₋₃₀ alkyl or C₃₋₃₀aryl; a cyano group; a thiol; a sulfide; a silicon-containing group suchas a C₁₋₃₀ alkylsilane, or C₆₋₃₀ arylsilane; a carboxyl containing groupsuch as an aldehyde, ketone, carboxylic acid, ester, or amide; an ether;or a combination comprising at least one of the foregoing. In anexemplary embodiment, the functional group may be a phenyl,4-methoxyphenyl, hydroxyphenyl, methyl, ethyl, n-propyl, 2-propyl,n-butyl, 2-butyl, isobutyl, or a combination comprising at least one ofthe foregoing. Optionally, a pendant photoacid generator may further beincluded as a functional group in the acid sensitive copolymercomposition. It will be understood that the acid decomposable groups,attachment groups, and functional groups may be included bycopolymerization of corresponding functionalized styrene, olefinic,vinylic, or (meth)acrylate monomers.

In an embodiment, the acid sensitive copolymer has the structure offormula 1:

wherein R₁ is a C₁₋₃₀ acid decomposable group comprising a tertiaryalkyl ester group, R₃ is a C₁₋₃₀ attachment group comprising a hydroxygroup, R₅ and R₇ are independently a C₁₋₃₀ functional group comprisingan aromatic group or an ester group, R₂, R₄, R₆ and R₈ are independentlyH or a C₁₋₁₀ organic group, mole fractions w and x are 0.001 to 0.999and mole fractions y and z are 0 to less than 0.9, where the sum of molefractions w, x, y, and z is 1. In a specific embodiment, mole fraction xis 0.05 to 0.65, mole fraction y is 0.35 to 0.95, and mole fraction z is0 to 0.90, where the sum of mole fractions x, y, and z is 1.

In a specific embodiment, the acid sensitive copolymer has the structureof formula 2:

wherein R₉ is a C₁₋₂₀ acid decomposable group comprising a tertiaryalkyl ester group, R₁₀ is H or a C₁₋₃₀ alkyl group, R₂, R₄, and R₆ areindependently H, methyl, ethyl, or phenyl, mole fraction x is 0.05 to0.65, mole fraction y is 0.35 to 0.95, and mole fraction z is 0 to 0.9,where the sum of mole fractions x, y, and z is 1.

In an exemplary embodiment, the acid sensitive copolymer has formula(3):

where mole fraction a is 0.05 to 0.65, and mole fraction b is 0.35 to0.95, and the sum of mole fractions a and b is 1.

In another exemplary embodiment, the acid sensitive copolymer hasformula (4):

where mole fraction a is 0.05 to 0.65, mole fraction b is 0.15 to 0.75,and mole fraction c is 0.20 to 0.80, and the sum of mole fractions a, b,and c is 1.

In another exemplary embodiment, the acid sensitive copolymer hasformula (5):

where mole fraction a is 0.05 to 0.65, mole fraction b is 0.15 to 0.75,and mole fraction c is 0.20 to 0.80, and the sum of mole fractions a, b,and c is 1.

In another exemplary embodiment, the acid sensitive copolymer has thestructure of formula (6):

wherein R₁₁ is a C₁₋₂₀ acid decomposable group comprising a tertiaryalkyl ester group, R₁₂ is a C₁₋₃₀ hydroxy-containing group, R₁₃ is H, aC₁₋₁₀ alkyl, or C₁₋₁₀ alkoxy; R₂, R₄, and R₆ are independently H,methyl, ethyl, or phenyl, mole fraction x is 0.05 to 0.65, mole fractiony is 0.35 to 0.95, and mole fraction z is 0 to 0.90, where the sum ofmole fractions x, y, and z is 1.

In an exemplary embodiment, the acid sensitive copolymer has thestructure of formula (7):

where mole fraction a is 0.05 to 0.65, mole fraction b is 0.15 to 0.75,and mole fraction c is 0.2 to 0.8, and the sum of mole fractions a, b,and c is 1.

In another exemplary embodiment, the acid sensitive copolymer has thestructure of formula (8):

where mole fraction a is 0.05 to 0.65, mole fraction b is 0.15 to 0.75,and mole fraction c is 0.2 to 0.8, and the sum of mole fractions a, b,and c is 1.

In another exemplary embodiment, the acid sensitive copolymer has thestructure of formula (9):

where mole fraction a is 0.05 to 0.65, mole fraction b is 0.15 to 0.75,mole fraction c is 0.2 to 0.8, mole fraction d is 0.1 to 0.6, and thesum of mole fractions a, b, c, and d is 1.

Additives to impart or enhance additional properties includingunderlayer properties or coating properties may be included in thesolution of the acid sensitive copolymer. Additives may includeadditional polymers, photoacid generators, thermal acid generators,surfactants including fluorinated surfactants, polyalkyleneoxysurfactants including polyethylene oxides, polypropylene oxides, andcopolymers of these; plasticizers' dissolution rate inhibitors (i.e.,compounds insoluble in aqueous base); dissolution rate enhancers (i.e.,compounds soluble in aqueous base); crosslinkers; catalysts; photocuringagents; adhesion promoters; amine quencher additives (for limiting aciddiffusion); or a combination comprising at least one of the foregoingadditives.

In an embodiment, the underlayer is a brush layer formed by directlydisposing the acid sensitive copolymer composition on the substratesurface and effecting a bond to the substrate (e.g., ionic,coordinative, or covalent). Alternatively, the underlayer is a mat layereither covalently bonded or not covalently bonded to the substrate. Themat layer may include, in addition to the acid sensitive copolymer, acrosslinking component and as needed, a catalyst. In one embodiment, thecrosslinking component may be a crosslinker. An exemplary acid-catalyzedcrosslinker includes an alkoxymethylglycoluril crosslinker such astetramethoxymethyl or tetrabutoxymethyl glycoluril. Where thecrosslinker is an acid-catalyzed crosslinker, an acid such asp-toluenesulfonic acid or its ammonium salt, or a thermal acid generatorsuch as the p-nitrophenyl ester of p-toluenesulfonic acid, may beincluded. Alternatively, the acid sensitive copolymer itself may furtherinclude a monomer capable of forming a crosslink with itself or anotherfunctional group on another monomer in the polymer, such as a hydroxy orcarboxylic acid group. Exemplary such crosslinking monomers includeepoxy-containing monomers such as glycidyl(meth)acrylate, or atrialkoxysilane-containing monomer such astrimethoxysilylpropyl(meth)acrylate as recited above. Where a mat layerrequiring an additional component is used, the acid sensitive copolymermay be present in an amount of 50 to 100 wt %, specifically 60 to 99 wt%, more specifically 70 to 95 wt %, and still more specifically 70 to 90wt %. Also in the mat layer, a crosslinker may be present in an amountof 0 to 50 wt %, specifically 1 to 40 wt %, more specifically 5 to 30 wt%, and still more specifically 10 to 30 wt %. A catalyst, where used,may be included in an amount of 0.1 to 5 wt %. All amounts are based onthe based on the total solids content of the mat layer.

In an embodiment, the underlayer further includes a photoacid generator.The underlayer is patterned by disposing an underlayer comprising thephotoacid generator on a substrate, irradiating the underlayer withactinic radiation in a pattern to generate acid in the exposed areas.

In this way, directly irradiating the underlayer with actinic radiationgenerates acid proximate to the acid sensitive groups. The acidsensitive groups of the acid sensitive copolymer in the underlayer thenreact with the diffused acid to form a polar region at the surface ofthe underlayer, the polar region having the shape and dimension of thepattern.

Any suitable photoacid generator may be included in the underlayerprovided the acid generated by the photoacid generator in the exposedportions of the photosensitive layer has an intrinsic pKa and mobilitywithin the underlayer that is sufficient to diffuse to, react with anddecompose the acid sensitive group of the underlayer, under theprocessing conditions.

The photogenerated acid from decomposition of the photoacid generatormay thus have a pKa of less than or equal to 3, specifically less thanor equal to 1, and still more specifically less than or equal to 0. Thephotoacid generator must also be thermally stable to temperatures of upto 250° C. for time periods of up to 10 minutes.

The photoacid generator, included in the photosensitive layer, can intheory generate one equivalent of acid upon absorbance of a quantum oflight of an appropriate wavelength, with accompanying by-products.Photoacid generators useful in the photosensitive layer includearyl-based onium salts including include mono-, di- andtriarylphosphonium salts, mono- and diaryliodonium salts, sulfonateesters including nadimidosulfonates, aromatic ketones such as benzoinderivatives, or a combination comprising at least one of the foregoing.In an embodiment, where the photoacid generator is included in theunderlayer, an aryl-based onium salt such as a mono-, di-, ortriarylsulfonium salt or a mono- or diaryliodonium salt having a highthermal stability (relative to, for example, a nadimidosulfonate ester)is used. Exemplary photoacid generators include triphenylsulfonium,n-octylphenyl(diphenyl)sulfonium, and di-t-butylphenyliodonium salts, ornadimidosulfonate esters, of acids such as methanesulfonic acid,benzylsulfonic acid, trifluoromethanesulfonic acid (triflic acid),perfluorobutanesulfonic acid, perfluorobenzenesulfonic acid,trifluoromethylbenzenesulfonic acid, perfluoroethylcyclohexanesulfonicacid, cyclo(1,3-perfluoropropanedisulfonium)imide, or a combinationcomprising at least one of the foregoing. Specific, non-limitingexamples of useful photoacid generators include triphenylsulfoniumtriflate, triphenylsulfonium perfluorobutanesulfonate,triphenylsulfonium o-trifluoromethylbenzenesulfonate, triphenylsulfoniumperfluorobenzenesulfonate, triphenylsulfoniumcyclo(1,3-perfluoropropanedisulfonium)imidate, di-t-butylphenyl iodoniumtriflate, di-t-butylphenyl iodonium perfluorobutanesulfonate,di-t-butylphenyl iodonium o-trifluoromethylbenzenesulfonate,di-t-butylphenyl iodonium perfluorobenzenesulfonate, or a combinationcomprising at least one of the foregoing.

The photoacid generator may be present in the underlayer in an amount of0.1 to 10 weight percent (wt %), specifically 0.5 to 8 wt %, morespecifically 1 to 7 wt %, and still more specifically 1 to 5 wt %, basedon the total solids content of the underlayer.

The underlayer is formed by contacting a solution comprising the acidsensitive copolymer and photoacid generator composition to thesubstrate. Contacting may be done by spin coating, spray coating, dipcoating, or doctor blading.

In an embodiment, the substrate is a semiconductor substrate andcontacting is by spin coating. Spin coating comprises dispensing asolution of the acid sensitive brush copolymer onto a surface of thespinning semiconductor substrate. The acid sensitive copolymer isdissolved in a solvent useful for film forming, at a concentrationuseful for spin-casting and film forming. Exemplary solvents mayinclude, but are not limited to, 1-methoxy-2-propanol,1-methoxy-2-propyl acetate, ethyl lactate, anisole, cyclohexanone,2-heptanone, diacetonealcohol, or a combination comprising at least oneof the foregoing. The concentration of the acid sensitive copolymer inthe solution may be less than or equal to 40 wt %, and in an embodiment,may be from 0.1 to 30 wt %, specifically 0.5 to 20 wt %, and still morespecifically 1 to 10 wt %, based on the total weight of the solution.

In an embodiment, the underlayer is applied by spin coating. Conditionsfor spin coating, where used, are dependent on the substrate diameterand other factors including desired film thickness which depends on thesolids content and viscosity of the formulation coated. Spin coating maybe carried out at a spin speed of 500 to 4000 rpm, specifically 800 to3000 rpm, and more specifically 1000 to 2500 rpm.

The underlayer is then heated by baking on a hot plate to removesolvent, condense the film by reducing free volume within the film, andto crosslink and/or attach the acid sensitive polymer to the substrate.Baking of the film may be carried out at a temperature of 50 to 200° C.,specifically 60 to 175° C., and more specifically 70 to 150° C. Aspecific time period for baking is 30 seconds to 5 minutes, morespecifically 30 seconds to 3 minutes, and still more specifically 30seconds to 2 minutes. The brush layer may further be annealed by bakingat a temperature of 100 to 300° C., specifically 125 to 275° C., andmore specifically 150 to 250° C. A specific time period for annealing is5 minutes to 10 hours, more specifically 10 minutes to 8 hours, andstill more specifically 15 minutes to 6 hours.

The underlayer, and specifically the acid sensitive copolymer, whenheated, may attach to the substrate by forming bonds between theattachment groups and the substrate. For example, the acid sensitivecopolymer may attach to a substrate having surface hydroxy groups, via ahydroxy containing attachment group, to form e.g., a silyl alkoxidelinkage where the substrate comprises silicon dioxide (as either thesubstrate itself, or as a layer of thermally grown or native oxide, or aspin-on glass, etc.). The substrate having the underlayer so attached isthen washed with a solvent to remove any residues of the acid sensitivecopolymer. Alternatively, where a mat layer is used, the acid sensitivecopolymer crosslinks either by direct polymer-to-polymer crosslinks, orthrough intermediacy of a crosslinking agent, to form interpolymercrosslinks. The resulting mat layer may or may not be bonded to thesubstrate.

The underlayer containing the photoacid generator is irradiated in apattern with actinic radiation. Actinic radiation, useful to generateacid by the photoacid generator is used, where it will be appreciatedthat the photoacid generator used in the underlayer is sensitive to theradiation wavelength used. The actinic radiation may be, for example,ultraviolet (UV) light having a wavelength of 10 to 400 nm, specificexamples of which are i-line radiation of 365 nm, deep ultraviolet (DUV)radiation at 248 nm, 193 nm, 157 nm, and extreme UV radiation of 10-15nm; x-rays; or electron beam (e-beam).

In a specific embodiment, the photosensitive layer is a photoresistcomprising a photoacid generator. The photoresist is a DUV photoresistor a 193 nm photoresist irradiated at a wavelength of 248 nm or 193 nm,respectively.

The pattern formed on the photosensitive layer or the underlayercontaining the photoacid generator may have features which form aregular pattern with a dense pitch, i.e., a ratio of linewidth to spacewidth of 1:1 or more (e.g., 1.1:1, 1.2:1, 1.5:1, 2:1, etc.), asemi-dense pitch of less than 1:1 (e.g., 1:1.5) or a sparse patternhaving a pitch of 1:2 or less (e.g., 1:3, 1:4, etc.).

A sparse pattern can be formed on the neutral surface of the underlayerusing low resolution techniques such as patterns of dashes or dots,rather than using contiguous patterns as would be obtained usingunbroken lines. Upon forming the domains on these patterns, the domainsalign to dashes and/or dots as well as to lines, and due to the abilityof domains to align with regularity of size and shape to domains formedon the intermittent patterned regions, the aligned domains can formpatterns comparable to those formed on contiguous patterns.

Advantageously, use of lines or dashes with high line-edge roughness andline-width roughness can correct any defects in domain alignment in a“self-healing” mechanism during annealing. In addition, for applicationsinvolving electron-beam lithography, writing dashed lines and/or dottedlines takes less writing time (and/or requires a lower energy dose) thanwriting a solid line, and so the cost and time for preparing the sparsechemical patterns with such non-contiguous lines can each beadvantageously reduced. Thus, in an embodiment, an irradiated patterncan be non-contiguous, comprising dashes and/or dots. The spacing andalignment of the dashes and/or dots are such that domains formed on thenon-contiguous pattern assemble to form a contiguous pattern of domainsin which the incidence of defects is minimized.

In an embodiment, thermal processing to effect a reaction betweenphotogenerated acid and the acid sensitive groups of the underlayer maybe carried out by hot plate, by oven/furnace, or other such heatingmethods. In an embodiment, thermal processing is carried out by heatingon a hot plate in a wafer processing and coating track. Heating by hotplate may be carried out under air or in an inert atmosphere such asunder nitrogen or helium. Thermal processing may be carried out atambient temperatures up to 250° C., for time periods of several secondsto several hours, depending on the temperature and the diffusionrequirements.

The acid contacting the underlayer in the exposed regions thendecomposes the acid decomposable groups on the acid sensitive copolymerto form polar groups defining the polar regions of the patternedunderlayer. The regions on the patterned underlayer not exposed tophotogenerated acid (i.e., those regions of the underlayer that were notirradiated and where the photoacid generator was not decomposed) remainneutral. In an alternative embodiment, the acid generated in theunderlayer in the exposed regions may act to catalyze formation of aneutral region by, for example, crosslinking, and the unexposed regionsmay be polar, in which instance the domains can align to the unexposedregions.

A self-assembling layer is then formed on a surface of the patternedunderlayer. The self-assembling layer comprises a block copolymer havinga first block with an affinity for the polar region of the underlayer,and a second, dispersive (also referred to as “neutral”) block withoutan affinity for the polar region of the underlayer. As used herein,“with an affinity for” means that the first block is surface-energymatched to the polar region and is attracted to the polar region, sothat during casting and annealing, the mobile first block depositsselectively on and aligns to the polar region. In this way, the firstblock forms a first domain on the underlayer that is aligned to thepolar regions of the underlayer (i.e., is aligned to the pattern formedby decomposition of the acid decomposable groups). Similarly, thesecond, dispersive block of the block copolymer, which has less affinityfor the polar region of the underlayer, forms a second domain on theunderlayer aligned adjacent to the first domain. “Domain”, as usedherein, means a compact crystalline or semi-crystalline region formed bycorresponding blocks of the block copolymer, where these regions may belamellar or cylindrical and are formed orthogonal to the plane of thesurface of the underlayer and in at least partial contact with theunderlying surface of the underlayer. In an embodiment, the domains mayhave a shortest average dimension of 1 to 100 nm, specifically 5 to 75nm, and still more specifically 10 to 50 nm.

The blocks can in general be any appropriate domain-forming block towhich another, dissimilar block can be attached. Blocks can be derivedfrom different polymerizable monomers, where the blocks can include butare not limited to: polyolefins including polydienes, polyethersincluding poly(alkylene oxides) such as poly(ethylene oxide),poly(propylene oxide), poly(butylene oxide), or random or blockcopolymers of these; poly((meth)acrylates), polystyrenes, polyesters,polyorganosiloxanes, polyorganogermanes, or organometallic polymersprepared from polymerizable organometallic monomers based on Fe, Sn, Al,or Ti, such as poly(organophenylsilyl ferrocenes).

In an embodiment, the blocks of the block copolymer comprise as monomersC₂₋₃₀ olefinic monomers, (meth)acrylate monomers derived from C₁₋₃₀alcohols, inorganic-containing monomers including those based on Fe, Si,Ge, Sn, Al, Ti, or a combination comprising at least one of theforegoing monomers. In a specific embodiment, exemplary monomers for usein the blocks can include, as the C₂₋₃₀ olefinic monomers, ethylene,propylene, 1-butene, 1,3-butadiene, isoprene, vinyl acetate,dihydropyran, norbornene, maleic anhydride, styrene, 4-hydroxy styrene,4-acetoxy styrene, 4-methylstyrene, or α-methylstyrene; and can includeas (meth)acrylate monomers, methyl(meth)acrylate, ethyl (meth)acrylate,n-propyl(meth)acrylate, isopropyl(meth)acrylate, n-butyl(meth)acrylate,isobutyl(meth)acrylate, n-pentyl(meth)acrylate, isopentyl(meth)acrylate,neopentyl (meth)acrylate, n-hexyl(meth)acrylate,cyclohexyl(meth)acrylate, isobornyl(meth)acrylate, orhydroxyethyl(meth)acrylate. Combinations of two or more of thesemonomers can be used.

Exemplary blocks which are homopolymers can include blocks preparedusing styrene (i.e., polystyrene blocks), or (meth)acrylatehomopolymeric blocks such as poly(methylmethacrylate); exemplary randomblocks include, for example, blocks of styrene and methyl methacrylate(e.g., poly(styrene-co-methyl methacrylate)), randomly copolymerized;and an exemplary alternating copolymer block can include blocks ofstyrene and maleic anhydride which is known to form a styrene-maleicanhydride diad repeating structure due to the inability of maleicanhydride to homopolymerize under most conditions (e.g.,poly(styrene-alt-maleic anhydride)). It will be understood that suchblocks are exemplary and should not be considered to be limiting.

Useful block copolymers include at least two blocks, and may be diblock,triblock, tetrablock, etc. copolymers having discrete blocks, each ofwhich block may be a homopolymer, or random or alternating copolymer.Exemplary block copolymers include polystyrene-b-polyvinyl pyridine,polystyrene-b-polybutadiene, polystyrene-b-polyisoprene,polystyrene-b-polymethyl methacrylate, polystyrene-b-polyalkenylaromatics, polyisoprene-b-polyethylene oxide,polystyrene-b-poly(ethylene-propylene), polyethyleneoxide-b-polycaprolactone, polybutadiene-b-polyethylene oxide,polystyrene-b-poly(t-butyl (meth)acrylate), polymethylmethacrylate-b-poly(t-butyl methacrylate), polyethyleneoxide-b-polypropylene oxide, polystyrene-b-polytetrahydrofuran,polystyrene-b-polyisoprene-b-polyethylene oxide,poly(styrene-b-dimethylsiloxane), poly(methylmethacrylate-b-dimethylsiloxane),poly(methyl(meth)acrylate-r-styrene)-b-polymethyl methacrylate,poly(methyl(meth)acrylate-r-styrene)-b-polystyrene,poly(p-hydroxystyrene-r-styrene)-b-polymethyl methacrylate,poly(p-hydroxystyrene-r-styrene)-b-polyethylene oxide,polyisoprene-b-polystyrene-b-polyferrocenylsilane, or a combinationcomprising at least one of the foregoing block copolymers.

The block copolymer desirably has an overall molecular weight andpolydispersity amenable to further processing. In an embodiment, theblock copolymer has a weight-averaged molecular weight (Mw) of 10,000 to200,000 g/mol. Similarly, the block copolymer has a number averagedmolecular weight (Mn) of 5,000 to 200,000. The block copolymer can alsohave a polydispersity (Mw/Mn) of 1.01 to 6. In an embodiment, thepolydispersity of the block copolymer is 1.01 to 1.5, specifically 1.01to 1.2, and still more specifically 1.01 to 1.1. Molecular weight, bothMw and Mn, can be determined by, for example, gel permeationchromatography using a universal calibration method, and calibrated topolystyrene standards.

The block copolymer is, in an embodiment, spin cast from a solution ontothe patterned surface of the underlayer to form a self-assembling layeron the surface of the underlayer. The block copolymer is heated to atemperature of up to 250° C. for up to 10 minutes to form the domains inan annealing process. The domains form where the first block forms afirst domain on the underlayer aligned to the polar regions, and thesecond block forms a second domain on the underlayer aligned adjacent tothe first domain. Where the irradiated portion of the underlayer forms asparse pattern, and hence polar regions, spaced at an interval greaterthan an interval spacing of the first and second domains, additionalfirst and second domains form on the underlayer to fill the intervalspacing of the sparse pattern. The additional first domains, without apolar region to align to, instead align to the previously formed second(dispersive) domain, and additional second domains align to theadditional first domains.

A relief pattern is then formed by removing either the first or seconddomain to expose an underlying portion of the underlayer. In anembodiment, the step of removing is accomplished by a wet etch method,developing, or a dry etch method using a plasma.

An exemplary method of an embodiment is illustrated in FIGS. 1A-1I.While the embodiment shown below is that of a brush layer, it will beappreciated that the underlayer may alternatively be a mat layercomprising an acid sensitive copolymer and a crosslinker, and which mayor may not be bonded to the substrate. FIG. 1A shows an unmodifiedsemiconductor substrate 100 having hydroxy groups 102 bonded to thesubstrate material 101. In an embodiment, the hydroxy groups 102 arereplaceable hydroxy groups, such as Si—OH groups (where the substrateincludes SiO₂) or Ti—OH groups (where the substrate includes TiO₂).

The polymer brush (i.e., the acid sensitive copolymer) is then attachedto the substrate, by a covalent bond. Where a mat layer is used (notshown), the mat layer may or may not be bonded to the surface of thesubstrate.

FIG. 1B shows the modified semiconductor substrate 210, in which thesemiconductor material 211 has been modified to include an acidsensitive copolymer 222 having acid sensitive groups 223, and connectedby bonding through alkoxy linkages to the semiconductor material 211 toform a underlayer 220. A photoacid generator 225, sometimes referred toherein as a “PAG”, is dispersed within the underlayer 220. PAG 225 isincluded with the acid sensitive copolymer in a solvent and the solutionis applied to the substrate. PAG 225 may be a discrete molecule,co-dissolved in the underlayer solution, or may be incorporated in theacid sensitive copolymer structure as a covalently or ionically attachedgroup.

Deposition of the underlayer is accomplished by, for example, spincasting a solution of the acid sensitive copolymer which comprises, inaddition to the acid sensitive groups 223, an attachment group having atleast one hydroxy group (not shown) as a terminal group of the polymerbackbone or as a terminal group in a side chain of the acid sensitivepolymer (e.g., where the acid sensitive copolymer compriseshydroxystyrene monomer or 2-hydroxyethyl methacrylate (HEMA) monomer asattachment groups). Heating to bond the underlayer 220 via theattachment groups may be carried out at any temperature and timesuitable to bond the acid sensitive polymer 222 to the semiconductormaterial 211. For example, bonding may be carried out on a hot plate ata temperature of 70 to 250° C., for a time of 30 seconds to 2 minutes.

The underlayer 220 is then washed to remove any unbonded acid sensitivecopolymer 222. Solvents for washing may include any solvent non-damagingto the acid sensitive groups, attachment groups, or functional groups orwhich would undesirably result in displacement of the bonded acidsensitive copolymer 222. Exemplary solvents may include toluene,anisole, PGMEA, cyclohexanone, or any solvent capable of removing theresidual acid sensitive copolymer. It is understood that where residualacid sensitive copolymer remains on the surface, the residual acidsensitive copolymer can become entrained in a subsequently appliedself-assembling layer which may fail to form phase-separated domains asa result.

PAG 225 is selected to have sufficient thermal stability to withstandthe incidental and cumulative heating processes the underlayer-coatedsubstrate (layers 210 and 220) is subjected to during processing.Desirable photoacid generators for use as PAG 225 may includearylsulfonium salts including mono-, di-, and triarylsulfonium salts,and diaryliodonium salts including mono- and diaryliodonium salts, wheresuch salts are sufficiently thermally stable to withstand in particularthe high temperatures (>100° C.) used to bond the acid sensitivecopolymer 222 to the semiconductor material.

The underlayer 220 is then patterned by irradiating with actinicradiation (hv). As illustrated in FIG. 1C, the underlayer 220 isirradiated through a reticle or mask 240 to form a pattern ofirradiation in the underlayer 220 by decomposition of the PAG 225 toform acid 226 in the irradiated region. Also in FIG. 1C (and subsequentFIGS. 1D to 1G), d represents the interval width, across the irradiatedsurface, of a repeating portion of the irradiated pattern including bothirradiated and non-irradiated regions.

In FIG. 1C, the irradiated underlayer 220 a contains acid 226 (H+) inthe irradiated portions which decomposes the acid decomposable groups223 in the irradiated portions of the underlayer 220 a. FIG. 1D showsthe resulting patterned underlayer 220 b, having polar regions of thepatterned underlayer 220 b comprising polar groups 224 in the reactedacid decomposable copolymer 222 b, and neutral regions of the patternedunderlayer 220 b having undecomposed acid decomposable groups 223 andundecomposed PAG 225 in the unreacted acid sensitive copolymer 222 a.Polar groups 224 in the polar region correspond to the irradiatedregions of the underlayer 220 as illustrated in FIG. 1C.

Diffusion of the acid generated from PAG 225 is limited to prevent unduebroadening of the pattern, and therefore the photoacid generatorselected for the patterned underlayer 220 b need not have a high acidmobility. For example, acids such as perfluorobutanesulfonic acid oro-trifluoromethylbenzene sulfonic acid may be used. It will also beappreciated that the acid 226 need only interact with acid sensitivegroups at or near the surface of the underlayer 220, sufficient toaffect the surface energy in the irradiated portion of the surface ofthe underlayer 220 forming the polar regions.

FIG. 1E next illustrates the disposition of a self-assembling layer 240on a surface of the patterned underlayer 220 b. The self-assemblinglayer 240 may comprise a block copolymer with blocks having differentsurface energies, where the blocks phase-separate and at least one blockforms a discrete domain aligned to the pattern, i.e., the region of thepatterned underlayer 220 b having the polar groups 224. Theself-assembling layer 240 is applied as a solution by spin-casting froma solvent, and after casting is heated to both remove residual solventand to compact and anneal the self-assembling layer. It is believed thatdomain formation, which requires mobility of the polymer chains to orderthe blocks of the block copolymer, occurs simultaneously with the lossof plasticizing solvent during heating and with ordering of the chainsof the individual blocks to form ordered cylindrical or lamellarstructures.

FIG. 1F illustrates the self-assembled layer 240 a after domainformation, having domains 241 a aligned to the polar regions (with polargroups 224) of patterned underlayer 220 a, and neutral domains 242 aaligned to polar domains 241 a and to the neutral regions (withundecomposed acid decomposable groups 223) of patterned underlayer 220a. It is noted that the interval of the irradiated regions is denoted byd in FIG. 1C to FIG. 1G, where d represents the interval width acrossthe irradiated surface of a repeating portion of the irradiated patternincluding both irradiated and non-irradiated regions. While FIG. 1Fexemplifies a patterned self assembly layer 240 a with interval d whichas illustrated corresponds to the width of combined domains 241 a and242 a, it will be understood that in other embodiments of a pattern, asparse pattern may be used.

FIG. 1G illustrates self assembly on a sparse pattern, i.e., one wherethe original irradiated pattern width d is greater than that of thecombined widths w of the polar and nonpolar domains (e.g., twice asgreat where 1 d=2 w, three times as great where 1 d=3 w, etc), ratherthan one in which the interval of the pattern equals the combined domainwidth (d=w). Thus, the interval d may coincide with the width w of thecombined domains or may exceed the width w (e.g., FIG. 1G, whichillustrates a 1 d=2 w ratio).

In FIG. 1G, where the sparse pattern is used, a polar domain 241 b ofself-assembled layer 240 b aligns to the polar region (having polargroups 224) of sparsely patterned underlayer 220 b, and a nonpolardomain 242 b aligns to the polar domain 241 b. A second polar domain 243b aligns to the nonpolar domain 242 b, where insufficient polar regionof the sparsely patterned underlayer 220 b is present, and anothernonpolar domain 244 b aligns to the second polar domain 243 b. Thepattern of alignment is then repeated across the surface of the imagedunderlayer. In this way, a sparse pattern can be used as a guide, incombination with the domain-forming tendencies of the self-assemblingblock copolymer, to multiply the pattern without need for irradiatingand transferring the complete pattern to the underlayer. This method isespecially efficient where dense line/space resolution is difficult toobtain in the irradiation step, or where the irradiation step is alengthy and time-consuming step (e.g., where e-beam direct writing isused).

FIG. 1H illustrates the formation of the pattern in relief. A domain 242a in the self-assembled layer 240 a from FIG. 1F is selectively removedto provide a pattern layer 250 a having positive pattern regions 251 aand spaces 252 a. Similarly, in FIG. 1I, the domain 241 a from FIG. 1Fis selectively removed to provide a pattern layer 250 b having positivepattern regions 251 b and spaces 252 b.

In either of the structures in FIG. 1H or 1I, the underlying nonpolarregion (FIG. 1H) or polar region (FIG. 1J) of the brush copolymer layer220 a may also be removed (not shown). Removal may be by a wet chemicaltreatment including dissolving the blocks, wet etching, or developingusing an acid or base developer, or may be accomplished by a selectivedry etching process.

The above methods and structures may be used in the manufacture ofsemiconductor devices including memory devices requiring denseline/space patterns such as synchronous dynamic random access memory(SDRAM) or dense features for data storage such as in hard drives. Itwill be appreciated that such devices are meant to be illustrative andshould not be construed as limited thereto.

The invention is further illustrated by the following examples.

All polymer compositions evaluated as underlayers were prepared asdescribed hereinbelow, except for polyhydroxystyrene (PHS), having an Mwof 10,000 to 25,000 and a polydispersity (Mw/Mn) of less than 2,obtained from Maruzen Corporation. Polymer composition was characterizedby ¹³C nuclear magnetic resonance (NMR) spectroscopy and by gelpermeation chromatography (GPC). NMR spectra were collected usingsamples dissolved in chloroform-d or acetone-d₆ with 0.9% chromium (III)acetylacetonate as a relaxation agent, with ¹H spectral data obtainedusing a 400 MHz Varian INOVA spectrometer with 10 second pulse delay,and ¹³C spectral data obtained using a 300 MHz Varian INOVA or 400 MHzBruker AVANCE 400 NMR spectrometer with a cryoprobe and 5 second pulsedelay.

Random copolymers of styrene, methyl methacrylate (MMA),hydroxyethylmethacrylate (HEMA), and tert-butyl acrylate (tBA) weresynthesized in tetrahydrofuran (THF) at 30 wt % solids via free radicalpolymerization. All copolymers were produced using the followingprocedure. The monomers were charged and the reaction mixture wasdegassed for 30 min., then allowed to equilibrate at 50° C. Uponequilibration, 80% of the targeted 1.50 mol % of VAZO 52 initiator wasadded. The reaction was heated to 67° C. for 1 h, after which theremaining 20% of the initiator was added. Temperature was maintainedovernight under reflux. The polymer was subsequently isolated byprecipitating into a 96:4 (w/w) ratio heptane/isopropanol (IPA) solutionand the polymer was collected by filtration and dried to constant mass.When the tBA content of the polymer was greater than 12 mol %, theheptane/IPA mixture was cooled with dry ice for at least 1 h prior toprecipitation.

The number-average molecular weight (M_(n)) and molecular weightdistribution (M_(w)/M_(n)) of the polymers were determined by gelpermeation chromatography, using a crosslinked styrene-divinylbenzenecolumn calibrated with polystyrene standards, and a sample concentrationof 1 mg/ml, with THF as eluant at a flow rate of 1 ml/min at 35° C.

The polystyrene-b-poly(methyl methacrylate) (“PS-b-PMMA”) copolymer usedin the study as the self-assembling copolymer was synthesized by anionicpolymerization as follows. An oven dried 1-liter, 3 necked round bottomflask was vacuum/purged with nitrogen and equipped with a magnetic stirbar, nitrogen/vacuum inlet, thermowell and a septum port. To the flask,dry THF (400 mL) and purified styrene (27.8 g, 0.27 mole) was added viacannula and the mixture was cooled to −70° C. Sec-butyllithium (0.71 gof a 0.47 mmole/g solution) was added quickly via cannula and there wasan immediate exotherm to −40° C. The reaction mixture turned anorange/red color. The reaction continued for 30 minutes, anddiphenylethylene (0.21 g, 1.22 mmole), dissolved in 5 mL dry THF andthen added to the reaction whereupon the reaction immediately turned adark red color. After 30 minutes, a solution of methyl methacrylate(12.79 g, 0.13 mole) in 20 mL of dry THF was added to the −70° C.reaction mixture, with subsequent exotherm to −62° C. accompanied by acolor change from dark red to light yellow. After 30 minutes, 2 mLanhydrous methanol was added to quench the reaction. The polymersolution was allowed to warm to ambient temperature and the reactionmixture poured into 1400 mL of stirring methanol. The precipitated solidwas isolated by filtration and dried in a vacuum oven at 60° C. for 16hours to constant weight, yielding 23 g (57% yield) of the polymer as awhite polymer.

For evaluation as brush layers, the (meth)acrylate polymers weredissolved in 2-heptanone (2 wt % based on the total solution weight).For evaluation as a mat layer, a formulation of 85 wt % of the aciddecomposable (meth)acrylate polymer, 11 wt % oftetra(methoxymethyl)glycoluril, 1 wt % of ammonium p-toluenesulfonate orp-toluenesulfonic acid, and 3 wt % of triphenylsulfoniumperfluorobutanesulfonate as a photoacid generator was prepared, anddiluted to 2 wt % total solids in 2-heptanone (based on the totalsolution weight). Both brush layer and mat layer formulations were caston unprimed 30 cm silicon wafers at 1500 rpm for 30 seconds, followed bya soft bake at 150° C. for 60 seconds to remove solvent and condense thefilm. The mat layer was then used directly in further evaluations,whereas the brush layer was additionally processed in an annealing stepby baking on a hot plate at 160° C. for 4 hours, to covalently bond theacid-decomposable (meth)acrylate polymer to the silicon wafer, and wassubsequently rinsed with 2-heptanone twice to remove any unbonded aciddecomposable (meth)acrylate polymer.

Measurement of the thickness of the resulting underlayer by atomic forcemicroscopy (AFM) showed a film thickness of 6-7 nm.

Contact angle was measured on a KRÜSS DSA Measurement Tool by theSessile prop method using both water (18 ohm deionized water) andmethylene iodide (CH₂I₂). Surface energy including both polar anddispersive components was calculated from the contact angles of each ofthese solvents using Fowke's method (a variant of the Owens-Wendtmethod). The surface energy results are reported in units of millijoulesper square meter (mJ/m²).

Copolymers of Ex. 1-4 and comparative copolymers CEx. 3 were prepared byradical polymerization according to the above method from styrene,2-hydroxyethyl methacrylate, methyl methacrylate, and/or t-butylacrylate in the molar proportions in Table 1. Note that thepolyhydroxystyrene (PHS) for CEx. 1 was used as obtained commercially,and that the poly(styrene-b-methyl methacrylate)diblock copolymer CEx. 2was prepared by the above described anionic polymerization method.

TABLE 1 Molecular Contact Surface energy Underlayer Polymer Weight angle(mJ/m²) Composition (mol %) (g/mol) (°) (dispersive/ Example PHS STYHEMA MMA t-BA Mn PD water CH₂I₂ dispersive polar polar) CEx. 1 100 — — —— — — 84 30.8 37 7 0.16 CEx. 2^(a) — 77 — 23 — 173,000 1.17 87.2 35.2 366 0.14 Ex. 1 — 74 9 5 12 27,500 2.28 82.5 42.2 31 9 0.22 Ex. 2 — 54 21 817 18,300 1.80 81.3 45.8 29 10 0.26 Ex. 3 — 77 2 — 21 15,200 1.29 85.735.2 36 7 0.16 Ex. 4 — 25 10 — 65 6,893 1.87 84.7 55.5 25 10 0.28 CEx. 3— 68 1.5 32 — 41,900 2.36 82.5 — — — — ^(a)Poly(styrene-b-methylmethacrylate) copolymer.

Brush layers were prepared as described above for the polymers inTable 1. As seen in Table 1, a polymer having a composition of 100%polyhydroxystyrene (CEx. 1) and which does not include an aciddecomposable group, exhibits dispersive and polar surface energies and apolarity ratio comparable to that of an exemplary diblock copolymer ofpoly(styrene-b-methyl methacrylate), used in a self-assembling layer(CEx. 2). Examples 1-4 each include acid decomposable groups (t-butylacrylate, abbreviated t-BA), a dispersive functional group (styrene,abbreviated STY), a hydroxy-functionalized reactive group(2-hydroxyethyl methacrylate, abbreviated HEMA), and Ex. 1 and 2 eachfurther included a filler monomer (methyl methacrylate, abbreviatedMMA). CEx. 3 contains STY, HEMA, and MMA but no t-BA. It can be seen inEx. 1, 2, and 4 that inclusion of higher amounts (10 mol % or more) ofHEMA increases the polar component of the surface energy resulting inthese copolymers deviating from a close match with CEx. 2 on thedispersive and polar surface energies, and resulting polarity ratios,and hence Ex. 1,2, and 4 are non-neutral and form a non-neutral surfacewith respect to the control CEx. 2.

However, the composition of Ex. 3 has the same dispersive surface energy(36 mJ/m²) and similar polar surface energy (7 mJ/m² for Ex. 3, comparedwith 6 mJ/m² for CEx. 2) and polarity ratio (0.16 for Ex. 3, comparedwith 0.14 for CEx. 2), and hence CEx. 2 and Ex. 3 are closely matchedand neutral toward one another.

A brush layer and a mat layer composition as described above, comprisingthe terpolymer of Example 1, having the following structure:

and formulated in 2-heptanone (2 wt % solids based on total solutionweight) were coated as described above to form a brush layer and a matlayer. The brush layer sample was coated with photoresist (EPIC™ 2340photoresist, available from Rohm and Haas Electronic Materials) to a 180nm film thickness and baked at 110° C. for 60 seconds. The wafers werethen exposed at 0, 125, and 250 millijoules per square centimeter(mJ/cm²) using a binary reticle consisting of an array of 180 nm contactholes at a 360 nm pitch across a 6.6 mm×6.6 mm field size, using annularillumination at a maximum numerical aperture (NA) of 0.75 for theexposure tool (ASML PAS 5500/1100 193 nm scanner, manufactured by ASML).After exposure, the photoresist sample was post exposure baked at 120°C. for 60 seconds, followed by developing in 0.26 N tetramethylammoniumhydroxide for 60 seconds. The photoresist was subsequently removed using2-heptanone.

Next, the block copolymer of CEx. 2, having the general structure:

was dissolved in 2-heptanone (2 wt % based on total solution weight) andwas spin cast to a thickness of about 100 nm on the 30 cm waferpreviously coated with the underlayer comprising the polymer of Example3 and imaged by the above method, and baked at 250° C. for 60 minutes toanneal the self-assembling layer and provide phase-separated domains ascylinders.

The PS-b-PMMA copolymer structures were analyzed using atomic forcemicroscopy (AFM) in tapping mode at a scanning rate of 0.5 Hz and adrive frequency of ˜270 Hz. The domain size and pitch of detectedfeatures was determined from a power spectral density (PSD) profile.

The samples having the cylindrical domains thereon were then imaged byAFM. FIG. 2 shows a series of AFM images of the samples in a 1 μm×1 μmscan area. The cylindrical domains can be seen in the figure for eachsample, and the domain dimensions for the figure are summarized in Table2, below.

TABLE 2 Exposure dose (mJ/cm²) 0 125 250 Brush Domain Size (nm) 43 ± 646 ± 5 45 ± 5 Pitch (nm) 77 77 74 Mat Domain Size (nm) 45 ± 5 44 ± 5 42± 4 Pitch (nm) 74 77 74Both underlayers (brush and mat), each with an acid sensitivemethacrylate copolymer composition (Ex. 3) matched to have approximatelythe same polarity ratio and to be neutral to the PS-b-PMMA copolymer,can provide phase-separated domains aligned to polar regions defined bythe exposed contact hole patterns. It can further be seen in FIG. 2 andTable 2 that the best defined features are obtained at lower exposuredose (125 mJ/cm²) than for the brush layer (250 mJ/cm²) in which theacid for deprotection of the (meth)acrylate copolymer of Ex. 1 isdiffused into the brush layer from the exposed regions of thephotoresist. In both the brush and mat layers, comparable feature sizeperformance is obtained. Advantageously, the mat layer (or a brush layercontaining a suitable thermally stable PAG) can be imaged directly,without need for the additional processing steps required for coatingand processing a photoresist as the deprotecting acid source for theunderlayer. Also advantageously, a mat layer does not require a lengthyannealing process for forming bonds to the substrate, or rinsing toremove unbonded brush layer polymer, further reducing the process cycletime per wafer.

All ranges disclosed herein are inclusive of the endpoints, and theendpoints are independently combinable with each other. The suffix “(s)”as used herein is intended to include both the singular and the pluralof the term that it modifies, thereby including at least one of thatterm. “Optional” or “optionally” means that the subsequently describedevent or circumstance can or cannot occur, and that the descriptionincludes instances where the event occurs and instances where it doesnot. As used herein, “combination” is inclusive of blends, mixtures,alloys, or reaction products. All references are incorporated herein byreference.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. Further, it should further be noted that the terms “first,”“second,” and the like herein do not denote any order, quantity, orimportance, but rather are used to distinguish one element from another.

1. A method of forming a pattern, comprising: irradiating a portion ofan underlayer comprising an acid sensitive copolymer comprising an aciddecomposable group, an attachment group, and a functional group, theattachment group being covalently bonded to a hydrophilic surface of asubstrate, crosslinked to form an interpolymer crosslink, or bothcovalently bonded to the surface of the substrate and crosslinked toform an interpolymer crosslink, and a photoacid generator, wherein theacid decomposable group reacts with an acid generated from the photoacidgenerator in the irradiated portion of the underlayer to form a polarregion at a surface of the underlayer, the polar region having a shapeand dimension of the pattern, forming a self-assembling layer on thesurface of the underlayer, the self-assembling layer comprising a blockcopolymer having a first block with an affinity for the polar region,and a second block having less affinity for the polar region than thefirst block, wherein first block forms a first domain aligned to thepolar region, and the second block forms a second domain alignedadjacent to the first domain, and removing either the first or seconddomain to expose an underlying portion of the underlayer.
 2. The methodof claim 1, wherein forming the underlayer comprises contacting asolution of the acid sensitive copolymer and photoacid generator to thesurface of the substrate by spin coating, dip coating, roll coating,spray coating, or doctor blading, heating to remove solvent and formcovalent bonds between the attachment group of the acid sensitivecopolymer and the hydrophilic surface, and washing the surface of theunderlayer with solvent to remove any unbonded brush copolymer.
 3. Themethod of claim 2, wherein forming the self-assembling layer comprisescontacting a solution of the block copolymer to the surface of theunderlayer by spin coating, dip coating, roll coating, spray coating, ordoctor blading, and annealing to remove solvent and form the first andsecond domains.
 4. The method of claim 1, wherein selective irradiationis accomplished by exposure of the portion of the underlayer withactinic radiation through a reticle, or by direct writing of a patternonto the irradiated portion of the underlayer by e-beam radiation. 5.The method of claim 1, wherein the irradiated portion of the underlayerforms a sparse pattern spaced at an interval greater than an intervalspacing of the first and second domains.
 6. The method of claim 5further comprising additional first and second domains formed on theunderlayer to fill the interval spacing of the sparse pattern, whereinthe additional first domains are aligned to the second domain but not toa polar region, and the additional second domain is aligned to theadditional first domain.
 7. The method of claim 1, wherein the photoacidgenerator is in admixture with the acid sensitive copolymer, or whereinthe photoacid generator is covalently bonded to the acid sensitivecopolymer.
 8. An underlayer comprising: an acid sensitive copolymercomprising an acid decomposable group, an attachment group, and afunctional group, and a photoacid generator, wherein the attachmentgroup is covalently bonded to a hydrophilic surface of a substrate byalkoxide linkages, is crosslinked to form an interpolymer crosslink, oris both covalently bonded to the hydrophilic surface of the substrateand crosslinked to form an interpolymer crosslink, and wherein the aciddecomposable groups are ester groups, acetal groups, ketal groups,pyrocarbonate groups, or a combination comprising at least one of theforegoing acid decomposable groups.
 9. The method of claim 8, whereinthe acid sensitive copolymer has the formula:

wherein R₁ is a C₁₋₃₀ acid decomposable group comprising a tertiaryalkyl ester group, R₃ is a C₁₋₃₀ attachment group comprising a hydroxygroup, R₅ and R₇ are independently a C₁₋₃₀ functional group comprisingan aromatic group or ester group, R₂, R₄, R₆, and R₈ are independently Hor a C₁₋₁₀ organic group, mole fractions w and x are 0.001 to 0.999,mole fractions y and z are 0 to 0.9, and the sum of mole fractions w, x,y, and z is
 1. 10. A self-assembled multilayer film, comprising: anunderlayer comprising an acid sensitive copolymer comprising an aciddecomposable group, an attachment group, and a functional group, and aphotoacid generator, wherein the underlayer is disposed on andcovalently bonded to a hydrophilic surface of a substrate, crosslinkedto form an interpolymer crosslink, or both covalently bonded to thesurface of the substrate and crosslinked to form an interpolymercrosslink through the attachment group, and portions of a surface of theunderlayer having the acid decomposable groups decomposed to form apatterned surface of the underlayer, and a self-assembling layerdisposed on the patterned surface of the underlayer, the self-assemblinglayer comprising a block copolymer having a first block with an affinityfor the portion of the surface of the underlayer having decomposed aciddecomposable groups, and a second block having less affinity for theportion of the surface of the underlayer having decomposed aciddecomposable groups than the first block, wherein the first block formsa first domain aligned to the portion of the underlayer having thedecomposed acid decomposable groups, and the second block forms a seconddomain on the surface of the underlayer aligned with and adjacent to thefirst domain.